The federal Nuclear Regulatory Commission (NRC) will soon put the Pilgrim nuclear power plant under closer oversight, following an unplanned shutdown last October.

The action, announced Wednesday by the NRC, comes two months after the agency declared Pilgrim “underperforming,” and the agency’s chairwoman said the plant’s owner Entergy was “going to have to work on it.”

Closer supervision will involve more NRC inspection, to determine the causes of Pilgrim’s poor performance.

The 685-megawatt plant will now be the eighth nuclear facility in the country in the “degraded” category. In 2011 the NRC shut down one of those plants, the Fort Calhoun station in Nebraska.

Pilgrim’s engineers and crews were forced to make the October “scram,” or unplanned shutdown, the night of Oct. 14, when the plant lost power from a 345-kilovolt NStar line that provides electricity to the plant.

That shutdown – the second such incident in 2013 – lasted a week.

Pilgrim was offline more than 80 days in 2013, with 46 of those days from scheduled refueling and maintenance.

In November, Entergy spokesman James Sinclair “said the company had conducted “rigorous reviews” of the shutdowns to identify needed improvements.

“Changes have been made in some key site leadership positions to accelerate our improvement,” Sinclair said at that time.

Pilgrim is one of the oldest operating nuclear power plants in the U.S. Built by Boston Edison, it went online in 1972. Entergy bought the plant in 1999 and secured a 20-year relicensing in 2012, after a six-year license review.S